648 LOWELL—MARS ON GLACIAL EPOCHS. [Nov. 16, 
tials are circumstanced nearly the same. In both planets the sol- 
stices fall not far from the line of apsides. What is more, it is the 
same solstice that occurs near perihelion in each case. Mars comes 
to perihelion in longitude 153° 4)’ and to the summer solstice of his 
northern hemisphere in longitude 176° 48’; our earth reaches the 
like points in her orbit, the perihelion in longitude 281° 21’, the 
summer solstice of her northern hemisphere in longitude 270° 14’ 
respectively. Thus both planets pass those points, whose near 
coincidence is vital to the effective working of the eccentricity, in 
close succession. With Mars the summer solstice follows perihelion ; 
with the earth it precedes it. This has the effect in the northern 
hemisphere of clipping the Martian beginning of summer as com- 
pared with its end, and of curtailing the mundane end of it as com- 
pared with its beginning ; similarly in the southern hemisphere of 
both with regard to winter. 
Curious it is that both planets should turn to the sun their corre- 
sponding hemispheres correspondingly—an agreement in inclina- 
tion which permits of paralleling, by what may at the moment be 
discerned on Mars, what would happen on the earth during an ac- 
centuation of eccentricity such as is invoked to account for a glacial 
period. It would show itself, too, under magnification. For the 
greatest maximum possible to the earth’s eccentricity is, according 
to Leverrier, .0747, or a fifth part less than that of Mars now. 
21. Having surveyed the situation, material and mechanical, we 
may now turn to the phenomena. When we do so we are con- 
fronted at once upon the planet by what appear to be unmistakable 
polar caps, fairly comparable with our own in size and behavior, 
but with a difference. Ours are first distinguished by their greater 
extension. In our northern hemisphere the ground in winter is 
covered by a permanent mantle of snow down to about latitude 45°. 
This represents our snow-cap at that season, as it would appear to 
an outsider. In this we live and move and have our being for some 
four months, and it is at least a pregnant thought that to such an 
outsider the highest development of life upon our planet should 
seem thus for nearly half the year to have its existence within the 
polar cap. It opens our eyes, abstractly as well as personally, thus 
for a moment to see ourselves as others see us. Our northern polar 
snow-cap, then, covers on the average round the globe 90° or more 
at its most. If we take occasional snowfalls into account the maxi- 
mum might be considerably stretched ; for snow sometimes not only 
